1. Field of the Invention
The present invention relates to an ink jet printing apparatus and a print position setting method capable of adjusting a relative print position between nozzle lines.
This invention is applicable to a wide range of equipment using a variety of print mediums such as paper, cloth, leather, nonwoven fabric, OHP sheets, and even metal. Among applicable equipment are office equipment, including printers, copying machines and facsimiles, and industrial manufacturing equipment.
2. Description of the Related Art
As an information output device in word processors, personal computers and facsimiles, printers (printing apparatus) that print information such as characters and images on sheet-like print mediums such as paper and films are in wide use.
A variety of printing systems are known. An ink jet system in particular, which ejects ink from a printing means (print head) onto a print medium, has come into widespread use because of its advantages, which include an ease with which the printing system size can be reduced, an ability to print a high-resolution image at high speed, a low running cost, low noise achieved by non-impact system, and an ease with which a color image can be printed by using multiple color inks.
In a printing apparatus of an ink jet system (hereinafter referred to as an “ink jet printing apparatus”), a print head (ink jet print head) may be used which has a plurality of lines of ink ejection nozzles. In such a print head, nozzle lines may have subtle variations in their positioning accuracy and there may also occur differences in ink ejection speed among different nozzle lines. Let us consider a case where such a print head is used on an ink jet printing apparatus of a serial scan type. If ink is ejected from the different nozzle lines onto a print medium at the same drive timing while the print head is moved in a main scan direction, ink landing positions on the print medium may deviate between the nozzle lines. This results in subtle deviations in relative print position between the different nozzle lines. If printing is performed with the relative print position deviated among the different nozzle lines, printed lines may fail to align or a density of dots formed on the print medium may vary depending on locations and ink colors, giving the printed image a granular impression.
Therefore, the relative print position between the nozzle lines needs to be adjusted (generally called “print position adjustment”) to improve the quality of printed images.
Such a print position adjustment is made as follows. First, nozzle lines are used to print on a print medium a plurality of print position adjustment patterns by differentiating their printing conditions. Then, from among the printed patterns a most desirable pattern is chosen and, based on the printing condition of the selected pattern, an inter-nozzle line printing condition is set. More specifically, two nozzle lines whose relative print position is to be adjusted are driven at such drive timings as will shift their relative print position progressively in a main scan direction to print a plurality of print position adjustment patterns on a print medium. From among the printed patterns, an optimum pattern is selected and, based on the drive timing used to print that pattern, the print position adjustment is made.
In an ink jet printing apparatus having a plurality of nozzle lines, as described above, the adjustment of relative print position between the nozzle lines can improve a quality of printed image.
A technique has been known which prints print position adjustment patterns by using a plurality of nozzle lines and, based on the printed result, performs a print position adjustment for each nozzle line. Japanese Patent Disclosure No. 61-222778, for example, discloses a method which causes each of multiple color head units to print a predetermined pattern to check for a presence or absence of a deviation between the head units. Japanese Patent Disclosure No. 04-041252 discloses a method which reads a predetermined pattern printed by each of a plurality of nozzle lines to automatically check for any positional deviation.
In recent years, for an improved quality of printed images, new printing techniques have come to be used, which include using many nozzle lines to eject various kinds of inks or multimode nozzle lines with different ink ejection amounts. Under these circumstances, there is a tendency for an increase in the number of equipped nozzle lines.
When the print position adjustment pattern is printed using each of the increasing number of nozzle lines, the number of patterns printed naturally increases and an amount of ink consumed in the pattern printing also increases. Further, this technique requires an additional process of selecting the best printed result from among many printed patterns. If this selection process is left to the user, this becomes an onerous burden for the user. This technique also requires calculating adjust values of print positions associated with the large number of nozzle lines, based on the printed result of these patterns, and setting again the drive timings of individual nozzle lines. This process also represents a large burden.